What is the shear rate at the pipe wall, in case of laminar flow of Newtonian fluids in a pipe of diameter 'D' & length 'L' incurring a pressure drop 'Δp' with average velocity 'Vavg' ?
Correct answer: C. 8 Vavg/D
- A. D Δp/8L
- B. D Δp/4L
- C. 8 Vavg/D
- D. 4 Vavg/D
Explanation
For laminar pipe flow, the wall shear rate is the velocity-gradient magnitude at the wall, equal to 8Vavg/D. Using the pressure-drop relation gives the equivalent form DΔp/(4μL), so option c is the only matching expression.
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